The first trailer hitches only consisted of a clevis and a pin, and later a ball mounted on the framework of a tow vehicle or a ball mount inserted into a receiver type hitch. These types of trailer hitches allowed for movement in all directions between the tow vehicle and the trailer. However, all that movement can negatively affect steering, braking, control, and overall vehicle performance. In addition, the increase in gross trailer weights over the years created the need for trailers that can handle different size weights, both large and small.
To accommodate different gross trailer weights, trailer hitches for light vehicles and trailers, such as autos, vans, SUV's, and pickup trucks, are generally one of four ratings, divided into Classes I-IV. For the purposes of this patent application, gross trailer weight is defined as the weight of the trailer when it is fully loaded. Ordinarily, hitches are rated for 10% of gross trailer weight to be on the tongue, referred to as the tongue weight. For the purposes of this patent application, tongue weight is defined as the weight put on a hitch ball by a trailer coupler.
A Class I hitch comprises a framework attached to a tow vehicle including a ball mount and ball for attaching a trailer coupler. This Class is generally rated at 2,000 lb. gross trailer weight. In addition, the ball mount can be either fixed or removable.
A Class II hitch is similar to Class I, except that the rating is generally 3,500 lb. Like Class I, Class II can have either a fixed or removable ball mount.
A Class III hitch only uses a removable ball mount. This style of hitch is known as a “hitch receiver”. In addition to ball mounts, a hitch receiver can be used with other more complicated types of mounts.
A Class IV hitch is similar to Class III, except it is heavier duty. This Class may be rated as high as 14,000 lbs. gross trailer weight.
To handle heavy trailer loads, a weight distribution hitch was invented. As trailer loads increase, tongue weight also increases. When tongue weight increases too much, it pushes down the rear of the tow vehicle causing numerous problems. To counteract this problem, the weight distribution hitch uses spring bars attached to a ball mount and a trailer frame to distribute the tongue weight among all the tow vehicle wheels and all the trailer wheels. As a result, the tow vehicle remains nearer to level from front to back while the trailer is attached. While this type of hitch is a big improvement over previous systems, it does very little to solve the problem of side-to-side movement of the trailer or sway, commonly called fishtail sway.
Fishtail sway is caused by the large distance between the rear axle of the tow vehicle and the hitch assembly and is aggravated by lateral forces against the vehicle caused by winds or passing vehicles. Previous attempts to solve fishtail sway involve stiffening the connection between tow vehicle and trailer by using various methods of friction. While these methods help some, none completely correct the problem.
Fortunately, in U.S. Pat. No. 4,722,542, hereafter referred to as the “Hensley hitch”, the sway problem is effectively corrected by forcing the hitch to turn through converging links that effectively move the pivot point between the tow vehicle and trailer to a point near the rear axle of the tow vehicle. Therefore, this design provides better steering and control of the trailer by eliminating trailer sway. While the converging links do this very well, the gross trailer weight is limited by the size and design of the converging links in '542 because so much of the tongue weight is supported by the converging links. As a result, increasingly heavier tongue weights require larger links, larger bearings, larger spindles, and larger related support systems. Increasing the size of these parts also increases both the hitch weight and the cost of manufacturing. In addition, the Hensley hitch needs workable brakes on the trailer controlled from the tow vehicle. Without trailer brakes or even with surge brakes the converging links tend to move to one side or the other due to the trailer pushing on the hitch assembly when the tow vehicle brakes are applied.
U.S. Pat. No. 5,660,409, hereafter referred to as the “Hensley mini-hitch”, does not need workable brakes on the trailer controlled from the tow vehicle. However, the Hensley mini-hitch is still limited to use on lighter trailers with relatively light tongue weight, because the tongue weight is supported by the on a sliding ball mount. In this design, a strut holds the trailer at a constant distance from the tow vehicle while stopping. In addition, a ball mounted on a sliding mount holds the trailer at a constant distance from the tow vehicle during turns. Still, this design requires maintaining this sliding mechanism as near a zero clearance as possible. To maintain this narrow clearance, fine-tuning and maintenance is required on the sliding mount. Nonetheless, this design is not practical for use with extremely heavy tongue weight.
Therefore, it would be advantageous to have a trailer hitch with a converging links design which does not support tongue weight with the converging links. A trailer hitch of this type could accommodate light and heavy trailer loads without the extra weight and cost associated with larger parts.